Transducer-induced heating-facilitated cleaning

ABSTRACT

In described examples, a transducer vibrates a lens element in a heating mode and a cleaning mode. Controller circuitry activates the transducer in the heating mode in response to an estimated temperature, and activates the transducer in the cleaning mode after the transducer is activated in the heating mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/463,840 filed Feb. 27, 2017, which is incorporated herein by reference in its entirety.

This application is related to coassigned U.S. patent application Ser. No. 15/887,923 filed Feb. 2, 2018 and coassigned U.S. patent application Ser. No. 15/903,569 filed Feb. 23, 2018, which are incorporated herein by reference in their entireties.

BACKGROUND

Electronic optical sensors are widely used for generating electronic images. Often, such sensors (e.g., “cameras”) are located in places remote to a viewer. The remote locations include places (e.g., external to vehicles) where contaminants (e.g. moisture and/or dirt) from the environment can cloud or otherwise obscure the camera lens, such that degraded images are generated by a camera having an obscured lens. The degradation of the image quality can decrease safety or security in many applications. Various techniques for automatically cleaning the camera lenses include water sprayers, mechanical wipers, or air jet solutions. Such approaches are not practical or too costly in a variety of applications.

SUMMARY

In described examples, a transducer vibrates a lens element in a heating mode and a cleaning mode. Controller circuitry activates the transducer in the heating mode in response to an estimated temperature, and activates the transducer in the cleaning mode after the transducer is activated in the heating mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example computing device for controlling a transducer coupled to a lens element.

FIG. 2 is a cross-section view of an example camera lens cover system.

FIG. 3 is a waveform diagram of an impedance response of an example camera lens cover system over a broad frequency range.

FIG. 4 is a waveform diagram of an impedance response of an example camera lens cover system over a reduced frequency range.

FIG. 5 is a plot diagram showing a linear relationship between the impedance response of an example camera lens cover system and operating temperatures thereof while operating at a selected operating frequency of 20 kHz.

FIG. 6 is a flow diagram of an example process for estimating a temperature of an example camera lens cover system in response to an impedance measurement of the example camera lens cover system.

FIG. 7 is an isometric view of an example camera lens cover system.

FIG. 8 is an external view of example foreign contaminant volumes for an example camera lens cover system.

FIG. 9 is a block diagram of an example signal generator of an example camera lens cover system.

FIG. 10 is a flow diagram illustrating an example method of foreign contaminant removal from an exposed surface of the example camera lens cover system.

FIG. 11 is a waveform diagram of impedance and phase response of an example camera lens cover system over a broad frequency range.

FIG. 12 is a top view of an example vehicle including example camera lens cover systems.

DETAILED DESCRIPTION

In this description: (a) the term “portion” means an entire portion or a portion that is less than the entire portion; (b) the term “housing” means a package or a sealed subassembly/assembly, which can include control circuitry, a transducer, lenses and an imaging sensor in a local environment that is sealed from an outside environment.

Ultrasonic vibration of lens surfaces (including lens covers) of camera systems (e.g. automotive systems including rear view and/or surround view systems) can be more cost effective than various water sprayer, mechanical wiper, or air jet solutions. As described herein, piezoelectric transducers (e.g., within a camera housing) can be monitored in a feedback loop structure without including a thermocouple in the feedback loop. The piezoelectric transducer is controlled by estimating a temperature of a piezoelectric transducer, such that, for example, the buildup of heat (which can be caused by activating the piezoelectric transducer) is limited by a comparison to a temperature threshold. The limiting of the buildup of heat helps prevent the permanent depolarization of the piezoelectric transducer (e.g., which could adversely affect the ability of the piezoelectric transducer to vibrate).

The apparatus and methods described herein for controlling and operating a piezoelectric transducer can help ensure that the temperature of the piezoelectric transducer does not reach more than one-half a Curie temperature (in degrees Celsius) of the piezo material of the transducer being controlled. In example embodiments, the transducer lifetime can be extended by the avoidance of operating the piezoelectric transducer at potentially damaging temperatures.

FIG. 1 is a block diagram of a computing device 100 for controlling a transducer coupled to a lens element. For example, the computing device 100 is, or is incorporated into, or is coupled (e.g., connected) to an electronic system 129, such as a computer, electronics control “box” or display, controllers (including wireless transmitters or receivers), or any type of electronic system operable to process information.

In example systems, a computing device 100 includes a megacell or a system-on-chip (SoC) that includes control logic such as a central processing unit (CPU) 112, a storage 114 (e.g., random access memory (RAM)) and a power supply 110. For example, the CPU 112 can be a complex instruction set computer (CISC)-type CPU, reduced instruction set computer (RISC)-type CPU, microcontroller unit (MCU), or digital signal processor (DSP). The storage 114 (which can be memory such as on-processor cache, off-processor cache, RAM, flash memory, or disk storage) stores one or more software applications 130 (e.g., embedded applications) that, when executed by the CPU 112, perform any suitable function associated with the computing device 100. The processor is arranged to execute code (e.g., firmware instructions and/or software instructions) for transforming the processor into a special-purpose machine having the structures—and the capability of performing the operations—described herein.

The CPU 112 includes memory and logic circuits that store information that is frequently accessed from the storage 114. The computing device 100 is controllable by a user operating a UI (user interface) 116, which provides output to and receives input from the user during the execution the software application 130. The UI output can include indicators such as the display 118, indicator lights, a speaker, and vibrations. The UI input can include sensors for receiving audio and/or light (using, for example, voice or image recognition), and can include electrical and/or mechanical devices such as keypads, switches, proximity detectors, gyros, and accelerometers. For example, the UI can be responsive to a vehicle operator command to clear an exterior surface of a backup camera of the vehicle.

The CPU 112 and the power supply 110 are coupled to I/O (Input-Output) port 128, which provides an interface that is configured to receive input from (and/or provide output to) networked devices 131. The networked devices 131 can include any device (including test equipment) capable of point-to-point and/or networked communications with the computing device 100. The computing device 100 can be coupled to peripherals and/or computing devices, including tangible, non-transitory media (such as flash memory) and/or cabled or wireless media. These and other such input and output devices can be selectively coupled to the computing device 100 by external devices using wireless or cabled connections. The storage 114 is accessible, for example, by the networked devices 131. The CPU 112, storage 114, and power supply 110 are also optionally coupled to an external power source (not shown), which is configured to receive power from a power source (such as a battery, solar cell, “live” power cord, inductive field, fuel cell, capacitor, and energy storage devices).

The transducer controller 138 includes control and signaling circuitry components for resonating a transducer of the lens cover system 132, such that the lens element can be cleaned by expelling foreign material (e.g., shaken clean of moisture). As described hereinbelow, the transducer controller 138 includes a temperature calculator 140 for determining a temperature of the lens cover system 132, such that, for example, the transducer of the lens cover system 132 is operated within a safe range of operating parameters.

FIG. 2 is a cross-section view of an example camera lens cover system. The camera lens cover system 200 generally includes a lens element 220, a seal 230, a housing 240, a transducer 250, and a camera 260. The camera 260 includes a camera lens 262, a camera base 264, a photodetector 272, and controller circuitry 274. The transducer 250 is operable to vibrate at a selected frequency (such as a factory-selected frequency or an operator-selected frequency) for motivating the dispersal of the moisture 210 (or other foreign materials) from the exterior (e.g., upper) surface of the lens element 220.

The lens element 220 is a transparent element elastically captivated in a distal (e.g., upper) portion of the housing 240. The lens element 220 is arranged to receive light from surrounding areas and to optically couple the received light to the photodetector 272 (e.g., via the camera lens 262). The lens element 220 is arranged to protect the camera lens 262 against moisture 210 intrusion, for example. The moisture 210 can be in the form of frost, water drops, and/or a film of condensation. Foreign materials (such as the moisture 210 and dirt particles) can block and/or diffuse light, such that at least some of the received light is prevented from reaching the camera lens (e.g., compound lens) 262. In an embodiment, the lens element 220 can be a focusing lens (e.g., for refractively focusing light).

A seal 230 (such as a rubber seal) is arranged to elastically captivate the lens element 220 to the housing 240 and to seal a cavity (e.g., in which the camera lens 262 is arranged) against intrusion of moisture 210 into the cavity. The intrusion of moisture 210 and other foreign substances into the cavity can facilitate condensation inside the lens cover system that can obstruct the camera's view. Moisture inside the lens cover system can also damage the controller circuitry 274 electronics and/or the pixels (e.g., pixel cells) of the photodetector 272. The cavity extends inwards from the lens element 220 to a proximal (e.g., lower) portion of the housing 240.

The cavity is also formed by the camera base 264, which is coupled to (or formed as part of) the housing 240. The camera base 264 can include a photodetector 272 and controller circuitry 274. The photodetector 272 can be a video detector for generating electronic images (e.g., video streams) in response to the focused light coupled through the lens element 220 and the camera lens (which can include lenses). The controller circuitry 274 can include: (a) a printed circuit board; (b) circuitry of the transducer controller 138; and (c) and the circuitry of the temperature calculator 140 for controlling the lens cover system 132 (e.g., where such circuitry and the lens cover system are arranged in a feedback loop structure). The controller circuitry 274 is coupled to external power, control, and information systems using wiring and/or optical conduits (such as fibers).

The transducer 250 is mechanically coupled to the lens element 220. The transducer 250 can be affixed to the lens element 220 by an intervening adhesive layer (e.g., a high-temperature resistant epoxy). In operation, the transducer 250 is arranged to vibrate (e.g., at a selected frequency) the lens element 220 in response to transducer driver signals. The transducer driver signals are controllably modulated, such that the transducer 250 is controllably excited in response to the transducer driver signals. The transducer driver signals can be amplitude modulated, such that vibrating lens element 220 can controllably expel moisture 210 and other such foreign material from the external surface of the lens element 220 (e.g., external to the cavity).

A lens cover system 132 can include the transducer 250, the housing 240, the seal 230, and the lens element 220. As described hereinbelow, the computing device 100 estimates the temperature of the lens cover system in response to (e.g., as a function of) electrical properties of the lens cover system. The computing device 100 controllably excites the transducer 250 in response to the estimated temperature to efficiently remove obscuring foreign material (including potentially obscuring foreign material) from the lens element 220 without exceed a threshold temperature limit. (For example, the transducer 250 can be destroyed or degraded when operated for prolonged periods at excessively elevated temperatures.)

The impedance response of the lens cover system 132 varies according to the temperature of the lens cover system 132. As described herein, the relationship between the estimated temperature of the lens cover system 132 and the measured electrical impedance of the lens cover system is substantially linear within a frequency range. FIG. 3, as described hereinbelow, shows an impedance response of an example lens cover system over a frequency range of selected temperatures.

FIG. 3 is a waveform diagram of an impedance response of an example lens cover system over a broad frequency range. The waveform diagram 300 includes a lens cover system impedance response 310. The lens cover system impedance response 310 shows the impedance in Ohms over a frequency range between 10 kHz to around 1 MHz. The example lens cover system can be a lens cover system, such as the system 200 described hereinabove.

The “zeros” of the impedance response correspond to the series resonance properties, which correspond to the electromechanical vibration properties (such as resonance) of a lens cover system that includes the example transducer. The electromechanical resonances of the system occur at frequencies in which relatively larger vibration amplitudes occur for a variable electrical input amplitude stimulus. For example, electromechanical resonances occur at frequency ranges 321, 322, and 323. The zeros are indicated by valleys (such as valley 301) in the curve 310. A reduced frequency range (e.g., for a “zoomed in” view) of the impedance response 310 is described hereinbelow with respect to FIG. 4.

FIG. 4 is a waveform diagram of an impedance response of an example lens cover system over a reduced frequency range. The waveform diagram 400 includes an example lens cover system impedance response 410. The lens cover system impedance response 410 shows the impedance response of the example lens cover system over a reduced frequency range (e.g., with respect to the frequency range shown in FIG. 3).

The lens cover system impedance response 410 includes discrete temperature curves for indicating the lens cover system impedance at a discrete temperature selected from a range of temperatures. The range of selected discrete temperatures extends from a temperature of − (minus) 40° C. to a temperature of 60° C., where the temperature represented by each temperature curve differs from the represented temperature of an adjacent temperature curve by 20° C. The range of temperatures encompasses operating temperatures potentially encountered in operation of the example lens cover system in various example applications.

For example, the temperature curve 412 shows the example lens cover system impedance response in Ohms over a frequency range of around 20 kHz to 40 kHz at a temperature of −40° C., whereas the temperature curve 414 shows the lens cover system impedance response in Ohms over a frequency range of around 20 kHz to 40 kHz at a temperature of 60° C. The lens cover system impedance response 410 includes a valley 401, which indicates a resonance of the example lens cover system at around 29 kHz for all illustrated temperature responses.

At frequencies below 150 kHz (e.g., as shown by the lens cover system impedance response 310), the gain of an impedance response generally decreases as the temperature increases, such that the gain of the lens cover system impedance response 410 is inversely related to temperature within a selected operating frequency range (e.g., with exceptions occurring around the locations of resonant frequencies of the example transducer). The change in the impedance over temperature is linear (e.g., having a constant slope and having a change in impedance that is proportional to a step change in temperature).

For example, the vertical spacing (e.g., for a given frequency) between each temperature curve between temperature curves 412 and 414 of a selected operating frequency is equal (e.g., substantially equal). The selected operating frequency is selected from a frequency included in a linear response region, such as the linear response region extending between, at least, 20 kHz and 25 kHz). The equal spacing of the temperature curves between temperature curves 412 and 414 is indicative of a linear relationship between an operating temperature and a measured impedance at a selected operating frequency.

The computing device 100 determines temperature of the example transducer in response to a measurement of the impedance of the example transducer. For example, the computing device 100 excites the example transducer to vibrate (e.g., in response to amplitude-modulated driver signals) at a frequency within a frequency range, so the transducer impedance varies linearly as a function of the frequency within at least part of the frequency range.

The dependent variable temperature T as a function of the impedance variable Z for the example transducer is expressed as the linear equation: T=−0.29*Z+392.6  (1) which has a coefficient of determination R² value of R²=0.9932 (e.g., which is substantially linear, and wherein the constant “−0.29” is a slope of the linear equation, and the constant “392.6” is a y-intercept of the linear equation). The dependent variable temperature T as a function of the impedance variable Z for the example transducer can also be expressed as the parabolic equation: T=A*Z ² +B*Z+C  (2) where A, B and C are constants. When A=0, Equation (2) is reduced to the linear form (such as the form of Equation (1)). Accordingly, the selected operating frequency is selected from within a frequency region within which the relationship between the estimated temperature and the measured impedance is determinable as a quadratic function (e.g., according to the Equation (2)).

The determined relationship between the estimated temperature of the lens cover system and the actual (e.g., empirically measured) temperature of the example lens cover system is substantially linear when the coefficient of determination R² value is at least 0.95, for example. As the value of the coefficient of determination R² approaches unity, the statistical variance between an estimated value using the linear equation and the actual value is minimized. As the value of coefficient of determination recedes from unity, errors in the estimation increase, which can result in any of: (a) decreased temperature operating range; (b) increased safety margins; and (c) decreased life of the lens cover system.

FIG. 5 is a plot diagram showing a linear relationship between the impedance response of an example lens cover system and operating temperatures thereof while operating at a selected operating frequency of 20 kHz. As described herein, the computing device 100 estimates the operating temperature of a lens cover system by measuring the impedance of the lens cover system at a selected operating frequency, and by converting the impedance measurement to an estimated temperature (e.g., according to the relationship described by Equation (1) hereinabove). The computing device 100 executes the conversion of the impedance measurement to an estimated temperature in response to calculating the Equation (1) result, and/or by indexing a lookup table to retrieve a result according to Equation (1).

Plot 500 shows the close statistical correlation between estimated curve 520 (EST) and a corresponding empirically measured curve 510 (MEAS). The actual (e.g., simulation value of) temperature is shown by the empirically measured curve 510. The estimated temperature (e.g., calculated using Equation (1)) is shown by the estimated curve 520. The computing device 100 estimates the curve 520 in simulations by controlling the temperature (e.g., from −60° C. to 40° C.) to derive impedance measurements (e.g., ranging from around 1150 Ohms to 1475 ohms) of the example lens cover system. The empirically measured curve 510 and the estimated curve 520 are statistically correlated to a high degree.

As shown by the plot 500, the relationship between the estimated temperature of the lens cover system and the actual (e.g., empirically measured) temperature of the example lens cover system is linear (e.g., substantially linear). The maximum error (e.g., determined in simulations between corresponding points of the estimated curve 520 and the empirically measured curve 510) shown by plot 500 is 3.7° C. Accordingly, the computing device 100 accurately estimates the lens cover system temperature using a simple linear equation.

For example, a temperature error 3.7° C. of a temperature estimate is sufficiently accurate, such that the example lens cover system can be safely operated when the transducer controller maintains the estimated operating temperature of the example lens cover system below a temperature threshold for estimated temperatures. As described hereinbelow, the computing device 100 selects the operating temperature threshold for estimated temperatures in response to the error margin of the estimated temperature measurement and the Curie temperature of the example transducer. The Curie temperature threshold can be a temperature threshold beyond which the permanent polarization of piezoelectric materials of the example transducer is degraded (for example, the Curie temperature threshold can be half of the Curie temperature). Accordingly, the temperature threshold is for delineating an operating temperature range (such as by delineating an upper and/or lower limit thereof), below which the example transducer can be activated without depolarization (e.g., accelerated depolarization).

In an embodiment, the computing device 100 measures the impedance data over a range of temperatures for a selected operating frequency at discrete temperatures, and the computing device 100 stores that data as a lookup table in memory (e.g., which reduces processing requirements for calculating the equation otherwise calculated to determine an instant operating temperature). The computing device 100 performs linear interpolation (e.g., one-dimensional linear interpolation) to more precisely determine the operating temperature (e.g., depending on a particular application of the described techniques, such as measuring a temperature outside a vehicle for determining a control decision described hereinbelow).

In an embodiment, the computing device 100 stores impedance data measured over a range of temperatures and over a range of operating frequencies. The computing device 100 measures impedance data at discrete temperatures and discrete operating frequencies, and the computing device 100 stores that data as a lookup table in memory (e.g., such that programmed firmware is not required for controlling specific transducers, each of which is operable at mutually different frequencies according to a selected transducer and a selected application). The computing device 100 performs linear interpolation (e.g., two-dimensional linear interpolation) to more precisely determine the operating temperature for a selected operating frequency.

FIG. 6 is a flow diagram of an example process for estimating a temperature of an example lens cover system in response to an impedance measurement of the example lens cover system. The computing device 100 can perform the flow 600 by hardware circuits exclusive of programming commands. For example, the example process can be executed by apparatus including analog and/or digital control circuits (such as registers, adders, multipliers, voltage generators, and comparators) that are arranged (e.g., pipelined) according to the process 600, described hereinbelow.

The flow 600 begins at operation 610, at which an example transducer is activated (e.g., electrically excited at a selected frequency by assertion of amplitude-modulated transducer driver signals). For example, the amplitude-modulated transducer driver signals are asserted to effect excitation of the example lens cover system at the selected frequency of 20 kHz (which is a frequency at which a linear relationship exists between the temperature of the example lens cover system and the impedance of the lens cover system). The flow continues to operation 620.

At operation 620, the impedance (e.g., effective impedance) of the activated example lens cover system is measured. In an examples, the computing device 100 measures impedance in response to a voltage drop resulting from coupling the example transducer to the asserted amplitude-modulated transducer driver signals. Because the example lens cover system is excited at 20 kHz, the measured impedance is derived in response to example transducer excitation at the selected frequency of 20 kHz. The flow continues to operation 630.

At operation 630, the measured impedance is converted to an estimated temperature. The estimated temperature is determined according to the linear relationship between the impedance of the example lens cover system and the operating temperature of the example lens cover system. For example, the computing device 100 converts the measured impedance to the estimated temperature by circuits operating according to the function of Equation (1), and/or the computing device 100 converts the measured impedance to the estimated temperature in response to indexing a lookup table with values for creating the output of Equation (1). The lookup table includes values that are addressable using the independent variable (e.g., the measured impedance) as the index, and that are output as results for providing or determining the value of the dependent variable. For example, the addressable values are determined (e.g., pre-calculated before or after deployment of the system 100) according to Equation (1). The flow continues to operation 640.

At operation 640, the temperature is compared against a temperature threshold. The computing device 100 determines temperature threshold in response to the Curie temperature threshold and a safety margin. The computing device 100 selects safety margin in response to the Curie temperature threshold, the maximum expected error of the estimated lens cover system temperature, and a margin for “derating” the lens cover system for increasing product lifetime (e.g., increasing the mean-time-between-failure reliability factor) of the example lens cover system. The flow continues to operation 650.

At operation 650, the activation state of the transducer is toggled (e.g., activated when the example transducer is in a deactivated state, or is deactivated when the example transducer is in an activated state) in response to the comparison at operation 640. For example, the example transducer is deactivated if the temperature indicates that the example lens cover system has an operating temperature that approaches a self-damaging temperature. The computing device 100 deactivates the example transducer when the comparison at operation 640 indicates that the estimated temperature exceeds half of the Curie temperature (in degrees Celsius) of the example transducer.

The computing device 100 performs the process 600 each time the example transducer is activated. For example, the computing device 100 may limit the length of a periodic interval (e.g., fixed period) of time during which the example transducer is activated, in order to periodically reperform the process 600 and thereby limit the accumulation of heat that results from activation of the example transducer. The computing device 100 deactivates the example transducer in response to expiration of a fixed period of time during which the example transducer is activated. The computing device 100 selects the length of time for limiting activation of the example transducer, in view of the rate of accumulation of heat during operation at the selected operating frequency and the relative sizes of safety margins. Accordingly, the computing device 100 controllably limits the rise of temperature of the example lens cover system, below levels that are likely to permanently (e.g., without repair) damage the example transducer (e.g., without incurring the space, cost and reliability considerations otherwise encountered by coupling a thermocouple to the example transducer).

FIG. 7 is an isometric view of an example camera lens cover system. The camera lens cover system 700 generally includes a transducer 710, power wires 720, a lens element 730 and bonding agent 740. The transducer 710 of the camera lens cover system 700 can be a cylindrical transducer, such as transducer 250 described hereinabove, which is arranged to apply ultrasonic vibrations for cleaning and/or heating a camera lens cover.

The transducer 710 is arranged to vibrate a mechanically coupled lens cover (e.g., the lens element 730) in response to being driven by an electronic amplifier at frequencies ranging from around 20 kHz to 2.0 MHz. The computing device 100 can drive the transducer 710 at a given excitation frequency, and the computing device 100 can sense a resulting impedance by coupling signals to and from the transducer via the power wires 720. The resulting impedance can be affected by temperature, mechanical characteristics, electrical characteristics and the frequency at which the transducer is driven, for example. A lens element 730 is secured to a distal surface of the transducer 710 by a bonding agent 740 (e.g. epoxy) disposed (e.g., as a circular shape) between the distal surface of the transducer 710 and an adjacent portion of a surface of the lens element 730. The seal between the transducer element and the lens element 730 helps prevent the intrusion of moisture into a sealed cavity (e.g., which can be formed by a camera base, the transducer 710, the lens element 730, and the bonding agent 740).

Environmental moisture (e.g., water drops, water droplets and/or a film of condensation) can adhere to an exterior surface of the lens element 730. The moisture can occlude light from being clearly received by a camera lens in the sealed cavity. The transducer 710 is operable to vibrate at a selected frequency for motivating the dispersal of the moisture (or other foreign materials) from the exterior (e.g., outer) surface of the lens element 730. When droplets of moisture and/or a film of condensation remain on the exterior surface of the lens element 730, the remaining moisture can cause saturation of the image sensor optically coupled to the camera lens when, for example, incident light encounters the exterior surface of the lens element 730 at an oblique angle.

The exterior surface of the lens element 730 can be formed without a “lip” (or can be formed with a lip arranged with channels extending therethrough), which provides a path for moisture migration during vibration. For example, vibration of the sealed lens element urges moisture along the path for moisture migration, because the vibration helps overcome surface tension of the moisture (which otherwise helps the moisture to adhere to itself and to the outer surface of the lens element 730). As described hereinbelow with respect to FIG. 8, the transducer 710 is arranged to (e.g., both) vibrate at the selected frequency and to generate thermal energy for heating the lens element 730.

FIG. 8 is an external view of foreign contaminant volumes for an example camera lens cover system. Water drops “contaminate” a lens surface (e.g., of lens element 730), such that a view through the lens surface is blocked or otherwise obscured. In an example, a camera lens cover system is vertically oriented, such that the lens element 730 is level, and such that moisture is not removed by gravity (e.g., for the purpose of illustration) during the moisture removal stages 810, 820, and 830. In the example, the multi-stage cleaning diagram 800 includes a large-volume cleaning stage 810 (e.g., for generally removing drops greater than around 15 μL in volume, such as drop 812), a medium-volume cleaning stage 820 (e.g., for generally removing drops less than around 15 μL in volume, such as drop 822), and a small-volume cleaning stage 830 (e.g., for removing residual moisture, such as droplets 832). Accordingly, a size of a foreign material is reduced by vibrating the lens element in the large-volume cleaning stage 810, the size of the foreign material is further reduced by vibrating the lens element in the medium-volume cleaning stage 820, and the size of the foreign material is even further reduced by vibrating the lens element in the small-volume cleaning stage 830.

In the large-volume cleaning stage 810, the transducer is arranged to vibrate in a first mode at a first selected frequency such that water drops of around 4-10 mm (or greater) diameter are dispersed (e.g., atomized or otherwise reduced in size) in response to vibration generated at the first selected frequency. In the first mode (in stage 810), a large-volume cleaning excitation signal is applied to the transducer to generate vibration at the first selected frequency. The first selected frequency can be a frequency in a frequency range at which electromechanical resonances occur. The first selected frequency can be characterized by a relatively high frequency vibration that consumes a relatively high amount of power. The large-volume cleaning stage 810 can be followed by the medium-volume cleaning stage 820.

In the medium-volume cleaning stage 820, the transducer is arranged to vibrate in a second mode at a second selected frequency, such that water drops (or droplets) of around 1-4 mm diameter are dispersed (e.g., atomized or otherwise reduced in size) in response to the vibration generated at the second selected frequency. In the second mode (in stage 820), a medium-volume cleaning excitation signal is applied to the transducer to generate vibration at the second selected frequency. The second selected frequency can be a frequency in a frequency range at which electromechanical resonances occur. The second selected frequency can be a frequency that is lower than the first selected frequency. The first selected frequency can be characterized by a relatively low frequency vibration that consumes a relatively low amount of power. The medium-volume cleaning stage 810 can be followed by a small-volume cleaning stage 830.

In the small-volume cleaning stage 830, the transducer is arranged to vibrate in a third mode at a third selected frequency, such that water droplets of around 0-1 mm diameter are evaporated (e.g., atomized or otherwise dispersed) in response to the heat and vibration generated at the third selected frequency. In the third mode (in stage 830), a heating excitation signal is applied to the transducer to generate vibration at the third selected frequency. The third selected frequency can be a frequency in a frequency range at which electromechanical resonances occur. For example, the water droplets of around 0-1 mm diameter are difficult to remove by vibrations, because of the water's surface tension and because of the relatively high van der Waals forces exerted between the surface of the lens cover and the water.

The third selected frequency can be a frequency that is higher than the first selected frequency. The third selected frequency can be characterized by a relatively high frequency vibration that consumes a relatively high amount of power. The heat generated by the transducer is thermally coupled to the lens element via the bonding agent 740 interposed between the transducer 710 and the lens element 730. The heat transferred to the lens element 730 helps remove any residual droplets, condensates on the lens element.

A control system described hereinbelow with respect to FIG. 9 is arranged to control the amount of heat generated so as to not overheat the piezoelectric material (which can damage the transducer actuator) and to avoid exceeding safe touch temperatures on the surface of the transparent element 730. The computing device 100 estimates the transducer temperature by measuring the impedance of the lens cover system as described hereinabove.

FIG. 9 is a block diagram of an example signal generator of an example camera lens cover system. For example, the signal generator 900 is arranged to control signals for driving a transducer of the lens cover system, to monitor the transducer performance and to change aspects of the drive signals in response to the monitored transducer performance.

The signal generator 900 includes a voltage (V) boost circuit 902 that is arranged to receive power (such as 12 volts direct current input from a vehicle power system) and to generate a 50-volt potential (e.g., surge-protected potential) from the received 12-volt input power. The 50-volt potential is modulated as described hereinbelow for driving a transducer of the camera lens cover system.

The signal generator 900 also includes an embedded core (such as a microcontroller unit MCU) 910 for executing instructions to transform the embedded core into a special-purpose machine for executing the functions of the camera lens cover system controller 920. For example, the camera lens cover system controller 920 includes control algorithms 922, pulse-width modulation (PWM) signal generation circuit 924, temperature estimation and regulation circuit 926 and system monitoring and diagnostics circuit 928. Such functions are described hereinbelow with respect to FIG. 10.

The camera lens cover system controller 920 is arranged to select operating parameters (such as cleaning modes, heating modes, cleaning stages, frequencies and operating temperatures) for the camera lens cover system in response to monitoring the camera lens cover system transducer and to control the PWM switching controller 930 in response to the selected operating parameters. For example, the camera lens cover system controller 920 is arranged to control PWM switching times of the PWM switching controller 930. The PWM switching controller 930 is arranged to signal the PWM PreDriver 940 in response to the switching times received from the PWM switching controller 930. The PWM PreDriver 940 generates control signals for toggling (e.g., actuating) the switches of the Class D driver 950. The Class D Driver 950 is a full-bridge rectifier that is arranged to generate +/−50 volts (e.g., 100 volts peak-to-peak) for driving the transducer 960. The sense circuitry 970 generate current and voltage signals for sensing impedance of the camera lens cover system and transducer 960, which are monitored (e.g., buffered) by the transducer monitor 980. The monitor signals are coupled via a multiplexer (MUX) 990 to the analog-to-digital converter (ADC) 990 for sampling. The embedded core 910 is arranged to receive the sampled current and voltage signals, to compute (via the camera lens cover system controller 920) new PWM signaling, to perform temperature estimation and regulation and to perform system monitoring and diagnostics as described hereinbelow with respect to FIG. 10.

FIG. 10 is a flow diagram 1000 illustrating an example method, performed by the computing device 100, of foreign contaminant removal from an exposed surface of the example camera lens cover system described herein. At 1002, the process begins in the camera lens cover system controller described hereinabove. At 1010, the camera lens cover system controller waits a period of time (e.g., waits for the system start signal) before identifying and/or determining the existence (presence) of contaminants at 1014. If the wait duration is not expired, the wait duration is updated at 1012, and the process loops back to 1010.

At 1014, after the wait period has expired, a frequency measurement device monitors the resonant frequency the example camera lens cover system to identify (for example) the amount of contaminant disposed on the exposed surface. For example, the computing device 100 determines the amount of a contaminant in response to a measured frequency response of the camera lens cover system and comparing the measured frequency response to a database that includes known frequency responses for given types and amounts for specific contaminants. At 1020, the camera lens cover system controller determines whether a contaminating material exists (is present) on the camera lens cover, such that at least one operation for cleaning the camera lens cover is initiated. If “YES,” then at 1028, the temperature of the example camera lens cover system is determined, and types of cleaning and heating are selected in response to the determined temperature as described hereinbelow. If “NO,” then system checks are performed at 1030.

If at 1020 the presence of a material is not indicated (“NO”), then at 1030, the process initiates system monitoring and diagnostics tests (e.g., during which the camera lens cover system is self-tested). At 1032, the computing device 100 decides whether to disable the system. For example, the computing device 100 decides whether to disable the system, in response to the nature of faults diagnosed at 1030, a response to a user input and/or a response to whether the power has been turned off to the system. If the system is to be disabled (“YES”), then at 1034, the system is shut down. If the system is not to be disabled (“NO”), the process loops back to 1010 and waits for a specified duration before the process starts again.

As described hereinabove, at 1028, the temperature of the example camera lens cover system is determined. For example, the computing device 100 determines the temperature of the example camera lens cover system in response to (e.g., as a function of) an operating frequency of an activated transducer as described hereinabove, or by a temperature sensing device (such as an externally coupled thermocouple). The process continues at 1050, for example.

If at 1050 the determined temperature is below the freezing point of water (e.g., within a margin of error), then at 1052, the camera lens cover system controller generates a heating signal for a specified duration (e.g., time period). For example, in response to a comparison of the determined temperature to the freezing point of water, the camera lens cover system controller can generate a heating excitation signal in a selected heating mode for warming the camera lens cover system as described hereinabove by exciting the transducer at a frequency at which the transducer generates relatively large amounts of heat, which occurs at frequency locations where the impedance response is small for a given voltage input. For example, the heating excitation signal in a heating mode for warming the camera lens cover system can be generated at a valley (such as the valley of the frequency range 321, which includes a relatively low impedance value of a selected frequency range) of a lens cover system impedance response curve (such as described hereinabove with respect to FIG. 3 and FIG. 4).

At 1054, the temperature of the example camera lens cover system is determined. After the temperature is determined (e.g., after initiation of a heating or cleaning mode), the process continues at 1040, after which the process initiates further operations (described hereinbelow) to ensure, for example, the transducer is operated within a safe operating region of temperatures.

If at 1056 the type and size of detected contaminating material indicates the contaminating material is to be reduced in size, then at 1058, a cleaning signal is generated for cleaning the example camera lens cover system. For example, the camera lens cover system controller can select a cleaning mode in response to the size of detected contaminating material. In selecting the cleaning mode, the computing device 100 can generate the cleaning signal as one of a large-volume cleaning excitation signal, a medium-volume cleaning excitation signal and a small-volume cleaning excitation signal. For example, the computing device 100 can generate: the large-volume cleaning excitation signal at a frequency conducive to resonating larger size drops of water; the medium-volume cleaning excitation signal at a frequency conducive to resonating medium size drops of water; and the small-volume cleaning excitation signal at a frequency conducive to heating small droplets of water. After the large-volume or medium-volume cleaning signal is generated and applied at 1058, the process continues to 1054 at which the computing device 100 determines the temperature of the example camera lens cover system (e.g., to ensure, the transducer is operated within a safe operating region of temperatures).

For example, if the size of detected contaminating material indicates small droplets of water at 1060, such that drying is indicated, then a heating signal is generated at 1062 for cleaning the example camera lens cover system. For example, the camera lens cover system controller can generate a heating signal in a heating mode, such that water droplets of around 0-1 mm diameter are evaporated (e.g., atomized or otherwise dispersed) in response to the heat and vibration generated, in response to the heating signal (e.g., applied at a frequency different from the respective frequencies of the applied cleaning signals). After the heating signal is generated and applied at 1062, the process continues at 1054 where the computing device 100 determines the temperature of the example camera lens cover system (e.g., to ensure, the transducer is operated within a safe operating region of temperatures).

After the temperature is determined (e.g., again) at 1054, the process continues at 1040, where the computing device 100 determines whether the temperature of the example camera lens cover system exceeds a temperature threshold. For example, the temperature threshold can be half of the transducer Curie temperature, such that the transducer is controlled to operate within a safe temperature range. If “YES,” the computing device 100 proceeds to disable the applied signal (e.g. heating or cleaning signal) at 1042. At 1044, the computing device 100 initializes cooling of the transducer and/or exposed surface (e.g., by entering a delay period during which the heating or cleaning signal is disabled, such that additional heat is not generated). At 1046, the computing device 100 determines the latest temperature, and in response at 1048, the computing device 100 determines whether the transducer temperature has finished cooling. For example, the computing device 100 can make the decision in response to the information determined at 1046, such that the temperature can be determined to be below a selected temperature threshold. In an example, the temperature threshold can be half of the transducer Curie temperature, such that the transducer is controlled to operate within a safe temperature range. In another example, the temperature threshold can be less than the transducer Curie temperature. If “YES” (e.g., when finished cooling), then at 1048, the process loops back to 1010. If “NO,” then at 1048, the process loops back to 1046, the computing device 100 determines a latest temperature, and the process loops back to 1048 (e.g., for additional cooling).

If “NO” at 1040 (e.g., when the transducer temperature does not exceed the temperature threshold), then at 1016, the computing device 100 determines whether the cleaning process is complete. If “YES,” then the process starts again at 1010. If “NO” at 1016, then at 1018, the computing device 100 updates the cleaning signal duration, and the process loops back to 1020 for additional testing and potential cleaning operations.

FIG. 11 is a waveform diagram of an impedance response of an example lens cover system across a broad frequency range. The waveform diagram 1100 includes a lens cover system impedance response 1110 and a phase response 1120. The lens cover system impedance response 1110 shows the impedance in Ohms across a frequency range between 10 kHz to around 1 MHz. The lens cover system phase response 1120 shows the phase shift in degrees across the frequency range between 10 kHz to around 1 MHz. The example lens cover system can be a lens cover system, such as the system 200 described hereinabove.

The “zeros” of the impedance response across a range of operating frequencies of the system correspond to series resonance properties of the example lens cover system. The series resonances of the system occur at frequencies in which relatively larger vibration amplitudes occur (and in which greater amounts of heat are generated within the transducer) for a variable electrical input amplitude stimulus. For example, electromechanical resonances occur at frequency ranges 1103, 1104, 1105 and 1106. The zeros are indicated by valleys (such as valleys 1113, 1114, 1115 and 1116) in the curve 1110. The computing device 100 selects the frequency range (and a valley therein) for assertion of a heating signal, in response to determining the magnitude (e.g., lowest magnitude) of an impedance across a range of possible operating frequencies. The computing device 100 selects a heating mode (e.g., frequency of a heating signal) in response to a determination of a valley of series resonances of the apparatus, wherein the series resonances are measured by the controller circuitry at various frequencies selected from a range of operating frequencies. Accordingly: (a) the computing device 100 measures an impedance-versus-frequency curve (e.g., 1110) in response to vibrating the lens element across a range of operating frequencies (e.g., 10 kHz through 1 MHz); (b) within that impedance-versus-frequency curve, at least one particular frequency of that vibration causes a respective valley (e.g., 1115) in the magnitude of the impedance; (c) a respective fixed bandwidth (e.g., frequency range 1105) encompasses that particular frequency; and (d) at least one example frequency of the heating signal is selected from within that respective fixed bandwidth.

The zeros are also characterized by relatively large phase shifts (such as a phase shift of over 100 degrees), wherein the instantaneous magnitude of the phase shift indicates the relative frequency location between a zero (at a lower frequency) and a pole (at a higher frequency) across a range of operating frequencies that includes: a phase peak; a proximate zero (e.g., the zero proximate to the phase peak); and a proximate pole (e.g., the pole proximate to the phase peak). The phase peaks 1123, 1124, 1125 and 1126 each occur within a respective relative frequency range 1103, 1104, 1105 and 1106, where each respective relative frequency range includes a valley (e.g., 1113, 1114, 1115 and 1116, respectively).

The computing device 100 detects the proximate zero associated with each of the phase peaks 1123, 1124, 1125 and 1126 by sweeping the operating frequency (e.g., downwards from a highest operating frequency). During the frequency sweep, the computing device 100 determines the phase peaks by tracking the resulting phase shift (e.g., by CPU 112 receiving signals from an ADC or a zero crossing detector). For example, as shown in FIG. 11, the frequency range 1105 includes: (a) a zero 1115 along the curve 1110; and (b) its associated phase peak 1125 along the curve 1120. Further, as shown in the example of FIG. 11, a frequency of the associated phase peak 1125 is approximately midway between: (a) the zero 1115; and (b) a pole of the curve 1110 within the frequency range 1105. In an example, the computing device 100 estimates the frequency of the proximate zero (e.g., at 1115) by: (a) evaluating an acceleration of the phase shift response 1120 across a lower frequency skirt (e.g., left skirt) of its associated phase peak (e.g., 1125); and (b) in response to that evaluating, determines such lower frequency skirt's inflection point (e.g., a point of a 45 degree slope). Accordingly, the computing device 100 selects the frequency of the heating signal from within a fixed bandwidth (e.g., frequency range 1105) that encompasses both the associated phase peak (e.g., 1125) and its lower frequency skirt's inflection point.

The computing device 100 determines relative impedances of various frequencies (e.g., estimated zeros) in response to comparisons of temperature measurements of heating generated by applied heating signals at different operating frequencies (although the different operating frequencies at which the heating signals are applied need not be associated with an estimated zero). For example, the computing device 100 can apply the heating signal at a frequency associated with at least one estimated zero, such that the computing device 100 determines the relative efficiency of the heating signal at the frequency associated with the estimated zero. The computing device 100 determines relative efficiency of the heating signal at the frequency associated with the estimated zero, by measuring a difference in temperatures sampled before and after the application of the heating signal. When temperature differences are determined for each of multiple zeros, the computing device 100 selects the zero associated with the greatest temperature difference as being a heating signal frequency (e.g., where greatest temperature difference indicates a low-impedance zero).

Accordingly, the computing device 100 selects a heating mode (e.g., including frequency range and a valley thereof) for assertion of a heating signal, in response to the detection of at least one zero by analysis of the phase response 1120. The selection of one of the lower magnitudes impedances can help ensure faster generation of heat, such that an example camera lens cover system can be more quickly thawed. The detection of the low-impedance zero (e.g., instantaneous series resonance) can be dynamically (e.g., in use, after deployment and/or in a calibration routine) determined by an ADC (such as ADC 992, described hereinabove) and a MCU (such as embedded core 910, described hereinabove).

FIG. 12 is a top view of an example vehicle including example camera lens cover systems. The vehicle 1210 includes a vehicle body that includes an interior space sheltered from an exterior environment. The vehicle 1210 includes at least one camera coupled to the vehicle body, where each camera includes a lens element, where the lens element is transparent and is exposed to the exterior environment. The vehicle also includes at least one apparatus that includes a transducer arranged to vibrate the lens element at a selected operating frequency when operating in an activated state.

The vehicle 1210 further includes controller circuitry 1250 coupled to the vehicle, wherein the controller circuitry 1250 includes a user interface arranged to receive commands generated in response to an operator operating the vehicle 1210 from the interior space of the vehicle, wherein the controller circuitry 1250 is arranged to measure an impedance of the apparatus while the transducer is operating at the selected operating frequency. The controller circuitry 1250 is arranged to determine an estimated temperature of the apparatus in response to the measured impedance and to generate a comparison of the estimated temperature of the lens element and/or transducer and a temperature threshold (e.g., for determining an operating mode and/or operating temperature range of the apparatus). The controller circuitry 1250 can also toggle an activation state of the transducer in response to comparing the estimated temperature of the apparatus against the temperature threshold.

For example, when the estimated temperature indicates an ambient temperature in which ice can exist, a heating signal is asserted before at least one cleaning signal is asserted. The heating signal can reduce frost into beads of water and/or vapor. The controller circuitry 1250 reduces residual beads of water by asserting at least one cleaning signal. Cleaning signals can be successively asserted at different frequencies by the controller circuitry 1250, such that larger beads of water are progressively reduced into smaller beads of water (as described hereinabove). For example, the controller circuitry 1250 asserts a heating signal as a drying signal to remove any residual beads and/or a film of water on the surface of the lens cover (as described hereinabove). The ambient temperature in which ice can exist can be a temperature at which ice (such as ice encountered on an example lens cover system) can remain frozen even after temperatures have risen above a freezing point of water (e.g., at atmospheric pressures in which a lens cover system is deployed). Accordingly, the controller circuitry 1250 compares the estimated temperature using a temperature threshold that is determined (by the control circuitry 1250) in response to a freezing point of water, and in response to other factors, such as (thermal time unit) degree-seconds (e.g., as determined from a temperature log), thermal capacity, relative wind velocity and ambient light.

In one example, the controller circuitry 1250 logs (e.g., samples at intervals and time stamps) temperature readings from lens cover system impedance measurements and/or other temperature sensors of the vehicle. Accordingly, the log of temperature samples includes information that indicates whether any of the logged temperatures are within a range of freezing temperatures. The controller circuitry 1250 can determine whether a likelihood exists of a presence of frost (e.g., frozen moisture) on a cover of a lens element of a lens cover system in response to: an estimated ambient temperature; the extent and lengths of time of the logged temperatures; analysis of an electronic image generated in response to light traversing the lens element; margins of error in temperature readings; and energies of phase change of water from solid to liquid. The analysis can include determining contrast ratios or other frequency information across all or some portions of the electronic image, wherein predominantly low frequency information in selected areas indicates the presence of frost at lower temperatures (e.g., close to or below freezing temperatures). In response to an indication that frost exists, the controller circuitry 1250 can select and assert a heating signal (such as described hereinabove with respect to operation 1052) to convert (e.g., thaw) frozen moisture on a lens element of a lens cover system into residual moisture. (Accordingly, the residual moisture includes previously frozen moisture.) The residual moisture can be progressively reduced by vibration (e.g., at operation 1058) and drying (e.g., any remaining residual moisture at operation 1062).

The controller circuitry 1250 can be arranged to measure an impedance of the apparatus in response to commands received from the operator operating the vehicle from the interior space of the vehicle 1210. The controller circuitry 1250 can also arranged to measure an impedance of the apparatus in response to the operator starting the vehicle 1210.

The controller circuitry 1250 includes a display 1260 (which can also include a touch screen) for displaying a synoptic view 1240 in response to each video signal of a local view 1230 of a local camera (CAM) 1220.

Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims. 

What is claimed is:
 1. An apparatus, comprising: a lens element; a transducer coupled to the lens element configured to vibrate the lens element at a first frequency and a different second frequency; and controller circuitry coupled to the transducer configured to: determine a first temperature of the lens element; generate a first comparison between the first temperature and a freezing point of water; responsive to the first temperature being less than the freezing point of water, activate the transducer by vibrating the lens element at the first frequency to thaw moisture on the lens element; after the lens element vibrates at the first frequency, responsive to thawed moisture on at least a portion of the lens element, activate the transducer by vibrating the lens element at the second frequency to reduce a size of the thawed moisture; determine a second temperature of the lens element; generate a second comparison between the second temperature and a depolarization temperature of the transducer; and responsive to the second temperature being greater than or equal to the depolarization temperature, deactivate the transducer.
 2. The apparatus of claim 1, wherein the transducer is configured to reduce a size of a foreign material on the lens element by vibrating the lens element at the second frequency, and the transducer is configured to further reduce the size of the foreign material by vibrating the lens element at a different third frequency.
 3. The apparatus of claim 2, wherein the foreign material includes moisture thawed responsive to the lens element vibrating at the first frequency.
 4. The apparatus of claim 3, wherein the controller circuitry is configured to activate the transducer to dry the lens element after reducing the size of the foreign material.
 5. The apparatus of claim 1, wherein the controller circuitry is configured to activate the transducer to dry the lens element by vibrating the lens element at the first frequency after vibrating the lens element at the second frequency.
 6. The apparatus of claim 5, wherein the controller circuitry is configured to generate at least one of the first or second comparisons responsive to logged temperatures.
 7. The apparatus of claim 6, wherein the controller circuitry is configured to select the first frequency responsive to an electronic image generated responsive to light traversing the lens element.
 8. The apparatus of claim 1, wherein the controller circuitry is configured to: measure an impedance of the transducer or the lens element; and determine at least one of the first temperature or the second temperature responsive to the measured impedance.
 9. The apparatus of claim 8, wherein the controller circuitry is configured to measure the impedance responsive to an excitation of the transducer by a pulse-width modulated excitation signal.
 10. The apparatus of claim 8, wherein the controller circuitry is configured to determine at least one of the first or second temperatures according to an equation T=A*Z ² +B*Z+C, in which Z is the measured impedance responsive to the transducer being activated, A is a constant, B is a constant, C is a constant, and T is the at least one of the first temperature or the second temperature.
 11. The apparatus of claim 1, wherein the lens element is configured to remove moisture from an exterior surface of the lens element by urging the moisture along a path for moisture migration responsive to the transducer vibrating the lens element.
 12. A system, comprising: a housing that shelters a space from an environment; a camera coupled to the housing, the camera including a transparent lens element exposed to the environment; an apparatus coupled to the housing, the apparatus including a transducer coupled to the lens element configured to vibrate the lens element at a first frequency and a different second frequency; and controller circuitry coupled to the housing, the controller circuitry configured to: determine a first temperature of the lens element; generate a first comparison between the first temperature and a freezing point of water; responsive to the first temperature being less than the freezing point of water, activate the transducer by vibrating the lens element at the first frequency to thaw moisture on the lens element; after the lens element vibrates at the first frequency, responsive to thawed moisture on at least a portion of the lens element, activate the transducer by vibrating the lens element at the second frequency to reduce a size of the thawed moisture; determine a second temperature of the lens element; generate a second comparison between the second temperature and a depolarization temperature of the transducer; and responsive to the second temperature being greater than or equal to the depolarization temperature, deactivate the transducer.
 13. The system of claim 12, wherein the controller circuitry is configured to determine at least one of the first or second temperature responsive to an impedance of the transducer or the lens element.
 14. The system of claim 12, wherein: the system includes a computing device coupled to the controller circuitry configured to measure an impedance-versus-frequency curve and a phase-versus-frequency curve responsive to the transducer vibrating the lens element across a range of operating frequencies; and the first frequency is within a fixed bandwidth that encompasses at least one of: a frequency corresponding to a valley on the impedance-versus-frequency curve; or a frequency corresponding to an inflection point of a lower frequency skirt associated with a phase peak of the phase-versus-frequency curve.
 15. The system of claim 12, wherein the controller circuitry is configured to select the first frequency by dynamically determining an instantaneous series resonance of the transducer or the lens element.
 16. The system of claim 15, wherein the controller circuitry is configured to select the first frequency by determining a frequency corresponding to a phase peak measured by a computing device in response to the transducer vibrating the lens element across a range of operating frequencies.
 17. A method, comprising: determining a first temperature of an apparatus that includes a lens element and a transducer coupled to the lens element configured to vibrate the lens element at a first frequency and a different second frequency; generating a first comparison between the first temperature and a freezing point of water; responsive to the first temperature being less than the freezing point of water, activating the transducer to vibrate the lens element at the first frequency to thaw moisture on the lens element; after operating the transducer at the first frequency, responsive to thawed moisture on at least a portion of the lens element, activating the transducer by vibrating the lens element at the second frequency to reduce a size of the thawed moisture; determining a second temperature of the apparatus; generating a second comparison between the second temperature and a depolarization temperature of the transducer; and responsive to the second temperature being greater than or equal to the depolarization temperature, deactivating the transducer.
 18. The method of claim 17, further including measuring an impedance of the apparatus when the transducer is activated.
 19. The method of claim 18, wherein determining the first temperature includes determining the first temperature responsive to the measured impedance.
 20. The method of claim 18, wherein determining the second temperature includes determining the second temperature responsive to the measured impedance.
 21. The method of claim 18, wherein: determining the first temperature includes determining the first temperature responsive to the measured impedance; and determining the second temperature includes determining the second temperature responsive to the measured impedance. 